Process for lining a metallic dry cell anode



Patented May 8, 1951 PROCESS FOR LINING A METALLIC DRY CELL ANODE Marcus R. Hatfield, L by mesne assignmen Carbon Corporation,

York

akcwood, Ohio, assignor,

ts, to

Union Carbide and a corporation of New No Drawing. Application November 16, 1946, Serial No. 710,402

The invention relates to galvanic cells of the dry type.

In the common form or" dry cell the anode is composed of zinc, and interacts with a self-depolarizing cathode consisting of a carbon rod surrounded by a mixture of carbon and manganese dioxide. The electrolyte comprises an aqueous solution of ammonium cloride and zinc chloride. Between the anode and the cathode there is a bibulous septum or diaphragm which usually includes a cereal paste, with or without a fibriform material such as paper or cloth.

In the application of Nelson C. Cahoon, Serial No. 568,137, filed December 14, 1944, now Patent No. 2,534,336 there is disclosed a dry cell in which the bibulous septum referred to above is composed of a cellulose ether, for example, an alkyl ether such as methyl cellulose. An object of my invention is to provide improved methods and compositions for preparing cellulose ether septa for dry cells. In accordance with my invention the septum can be made to surround a portion of the cell, and yet be seamless. In cells of conventional electrode placement, the septum envisaged by the invention will line the inside of the zinc cup anode, and surround the cathode and depolarizing mix; While in cells with a central anode, it will line the outside of the latter and thereby surround it. Cells of the kind last referred to are disclosed, for example, in an application of Paul A. Marsal, Serial No. 666,737, filed May '7, 194:6 now abandoned. The cells of the Marsal application have anodes provided with fins or vanes, and my invention affords a Way of lining them which avoids the difficulties encountered in wrapping them with preformed film.

In the practice of my invention a colloidal dispersion of a cellulose ether is applied to a dry cell anode in any suitable way, as by dipping, spraying, roller-coating, blade-coating or brushing. The suspending medium is then evaporated, leaving a bibulous solid, adherent, seamless film, sufiiciently rugged to withstand the operations involved in battery-manufacture, and sufficiently thick and continuous to perform the functions of an electrolytic diaphragm, yet so thin as to occupy but little space in the cell at the expense of the depolarizing mix.

The preferred cellulose ether is methyl cellulose. This material is insoluble in most organic solvents, but can be colloidally dispersed in certain of the lower alcohols, ketones, ethers, esters, etc. These media are referred to herein as oxygenated organic liquids of relatively low molecular weight. I prefer a dispersion in methanol 6 Claims. (Cl. 11774) containing about 5 per cent of the cellulose compound, but the concentration of the latter may be higher, for example 10 per cent; or it may be lower 'if a composition of lower viscosity is desired. An addition of Water, usually not exseeding 5 per cent, tends to thicken and stabilize the dispersion, and is often useful. Since the viscosity increases when the concentration of either methyl cellulose or water rises, comparable viscosities may occur when the sum of the percentages of these constituents is roughly constant. Moreover, an appropriate addition 01" water permits the preparation of dispersions in organic liquids such as ethanol and n-propanol, which solvate methyl cellulose less rapidly than does methanol.

The colloidal dispersions contemplated can be conveniently formed by milling the ingredients together in a ball mill. At the time of preparation, auxiliary constituents can also be incorporated. Mercury compounds are normally added to the diaphragm-material of a dry cell to eiiect amalgamation of the zinc, and this may be done with a cellulose ether suspension. Being an effective amalgamating agent yet relatively noncorrosive, mercurous chloride (calomel) is the preferred mercury salt. As a further safeguard against corrosion of spray nozzles and other metallic equipment, I prefer to add to the suspension a small amount of the ion-sequestering agent sold under the name Calgon for watersoftening and other purposes. This product is a complex sodium phosphate.

As is stated in application Serial No. 568,137, referred to above, methyl cellulose tends. to be softened by the electrolyte salts present in a dry cell, and particularly by zinc chloride, to such a degree that a septum or the unmodified material may be disrupted by diffusion and mechanical pressure until it no longer performs its intended function. As further stated in that application, the cellulose compound can be rendered more or less immune to this action, i. e. insolubilized, by a variety of hardening agents, including citric acid, phenol-formaldehyde resins, and urea-formaldehyde resins. Similar considerations apply to septa formed from colloidal dispersions. Hardening agents may be incorpo rated in the dispersions, and on evaporating the suspending medium and heating the film, they insolubilize the film to a degree determined by the nature and concentration of the hardening agent, and the intensity of the after-treatment. In a preferred form of the invention, one or more coats of unmodified methyl cellulose are applied to the anode, and after drying, one or more coats of insolubilized material are applied.

Before applying the suspension of methyl cellulose, the anode should be well cleaned. This can be done by any of the known methods for cleaning zinc surfaces. Securing with a wire brush followed degreasing has proved especially effective. The roughening resulting from wire-brushing promotes adhesion of the film.

Methyl cellulose is obtainable in a number of grades designated by the viscosities of their 2 per cent aqueous solutions at 20 C. These range from 15 to 4000 centipoises.

In a specific example of the invention the following suspensions were prepared:

A 100 cps. methyl cellulose (Dow Methocel) Three successive coats of suspension A were applied to clean zinc anodes by spraying, with drying after each application. Three coats of B were then similarly applied. Both suspensions were freshly prepared. The dry, coated anodes were then brought to 215 C., and held at that temperature for two minutes to insolubilize the outer layers. The total film was three mils thick, and entirely uniform and adherent. Dry cells made with the anodes prepared as above were exhaustively tested, as made, and after various periods of storage. Their performance was good in all respects.

The invention has important advantages. Not only are cells of excellent quality produced thereby, as stated above, but the lining of the anodes is carried out in an efiicient and economical way, well adapted to automatic machines. In lining anodes of which a section is a closed figure, such as the conventional cup-anodes or structures of Serial No. 666,737, the use of preformed film necessitates seams, which are undesirable. Moreover, a flat preformed film cannot easily be fitted to a warped anode surface. The invention permits a seamless and perfectly conforming lining to be applied to curved or warped anode surfaces of any kind.

the finned What is claimed is:

1. Process of lining a metallic dry cell anode which comprises applying to the active surface thereof a colloidal suspension of methyl cellulose in an organic liquid selected from the group consisting of low molecular weight alcohols, ketones, ethers, and esters, and drying.

2. Process of lining a metallic dry cell anode which comprises applying to the active surface thereof a colloidal suspension of methyl cellulose in methanol, and drying.

3. Process of lining a metallic dry cell anode which comprises applying to the active surface thereof a colloidal suspension of methyl cellulose in methanol, said suspension containing an insolubilizing agent for methyl cellulose, and drying.

4. Process of lining a metallic dry cell anode which comprises applying to the active surface thereof a colloidal suspension of methyl cellulose in methanol, said suspension containing a phenol-formaldehyde resin, and drying.

Process of lining a metallic dry cell anode which comp ises applying to the active surface thereof a colloidal suspension of methyl cellulose in methanol, drying, applying over the coating thus obtained a colloidal suspension containing methyl cellulose and an insolubilizing agent therefor, and again drying.

6. Process of lining a metallic dry cell anode which comprises applying to the active surface thereof a colloidal suspension of methyl cellulose in methanol, drying, applying over the coating thus obtained a colloidal suspension containing methyl cellulose and a phenolformaldehyde resin, and again drying.

MARCUS R. HATFIELD.

REFERENCES CITED following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,909,935 Dreyfus May 23, 1933 2,111,342 W'aldeck Mar. 15, 1938 2,231,319 Burgess Feb. 11, 1941 2,270,200 Upright Jan. 13, 1942 2,276,519 Sherk, et a1 Mar. 17, 1942 2,394,101 Phillips, et al Feb. 5, 1946 FOREIGN PATENTS Number Country Date 6,558 Australia Mar. 16, 1933 654,121 Germany Dec. 17, 1937 371,502 Great Britain Apr. 28, 1932 479,462 Great Britain Feb. 7, 1938 479,502 Great Britain Feb. 7, 1938 

5. PROCESS OF LINING A METALLIC DRY CELL ANODE WHICH COMPRISES APPLYING TO THE ACTIVE SURFACE THEREOF A COLLODIAL SUSPENSION OF METHYL CELLULOSE IN METHANOL, DRYING, APPLYING OVER THE COATING THUS OBTAINED A COLLOIDAL SUSPENSION CONTAINING METHYL CELLULOSE AND AN INSOLUBILIZING AGENT THEREOF, AND AGAIN DRYING. 